Pulse position dialing system with direct time measuring apparatus



l2 Sheets-Sheet` l .ES d

W. A. MALTHANER I'AL PULSE POSITION DIALING SYSTEM WITH DIRECT TIME MEASURING APPARATUS Nov. 3, 1953 Filed June 29, 1948 Nov. `3, 1953 W. PULSE P A. MALTHANER ETAL OSITION DIALING SYSTEM WITH DIRECT TIME MEASURING APPARATUS Filed June 29, 1948 12 Sheets-Sheet 2 sus.

ATTORNEY NOV- 3, 1953 w. A. MALTHANER ETAL 2,658,188

PULSE POSITION DIALING SYSTEM WITH DIRECT TIME MEASURING APPARATUS Filed June 29, 1948 l2 Sheets-Sheet 5 t A. mi. THANER /NVE/v Tons 1v. o. Newer H. E. val/GHAN- A T TORNE'V FIG. 41

By H. E. VUGHN IY. A. MAL THA/VER /NVEA/TORS N. D. NEWBY NOV- 3, 1953 w. A. MALTHANER ET AL PULSE POSITION DIALING SYSTEM WITH DIRECT TIME MEASURING APPARATUS Filed June 29, 1948 m. .ubi

Nov. 3, 1953 Filed June 29, 1948 W. A. MALTHANER ETAL PULSE POSITION DIALING SYSTEM WITH DIRECT TIME MEASURING APPARATUS l2 Sheets-Sheet 5 By f1.5. mus/MN A 7` TORNEV Nov. 3, 1953 Filed June 29, 1948 A. PULSE POS MALTHANER I'AL ITION DIALING SYSTEM WITH DIRECT TIME MEASURING APPARATUS l2 Sheets-Sheet 6 "f A.HALTHANER i /Nl/ENTORS- N. D. NEWBY H. E. VAUGHAN ATTOMEQ N0 3, 1953 w. A. MALTHANER ETAL Y 2,658,188

PULSE POSITION eDIALING SYSTEM WITH DIRECT TIME MEASURING APPARATUS Filed June 29, 1948 l2 Sheets-Sheet '7 I i Il I IIIIII 'I''I ssl/EN ou/v TER Mlm/MUM /NTERVAL T/MER t A. MA1. THA/VER /m/E/v T095 lv. o. /vEwsr H. E. vAuGf/A/v A 7' TORNEI FIG. 8

w. A, M-ALTHANx-:R E1- AL 2,658,188 PULSE POSITION DIALING SYSTEM WITH DIRECT TIME MEASURING vAPPARATUS Nov. 3, 1953 Filed June 29, 1948 12 SheetS-Sheet 8 /NARV COUNTER i A. NALTHANER /NVENTORS N. D. NEWBY H. E. VAUGHAN A TTORNEV w. A. MALTHANER ErAL 2,658,188 PULSE POSITION DIALING SYSTEM WITH DIRECT TIME MEASURING APPARATUS Nov. 3, 1953 l2 Sheets-Sheet 9 Filed June 29, 1948 NCQ AAA

Nov. 3, 1953 w. A. MALTHANER ET AL 2,658,188

PULSE POSITION DIALING SYSTEM WITH DIRECT TIME MEASURING APPARATUS Filed June 29, 1948 l2 Sheets-Sheet 10 imml is;

mavtl f AIMALTHANER /NVE/VTORS N. D. NE WBV H. E. VAUGHAN NOV. 3, 1953 w. A. MALTHANER ETAT. I 2,658,188

' PULSE POSITION DIALING SYSTEM WITH DIRECT TIME MEASURTNG APPARATUS i A. AIALTHANER /NVENTORS N. D. NEWBY ILE'. VAUGHAN www A T TOR/MEV NOV- 3, 1953 w. A. M'ALTHANER ETAL 2,658,188

PULSE POSITION DIALING SYSTEM WITH K DIRECT TIME MEASURING APPARATUS i A. NALTHANER /N VE N TOPS N. D. NEWBY H. E. VAUGHA/V atentec ov. 35, QS

UNITED STATES PULSE POSITION DIALING SYSTEM. WITH DIRECT' TIME MEASURIN G APPARATUS Summit, Nealv D. Newby,

William. A. Malthaner,

and Henry E. Vaughan, Chatham, N. J.,

Leonia,

assignors to Bellv Telephone Laboratories, Incorpora-ted, New York, N. Y., a. corporation of New York.

Application J une 29, 1948, Serial No. 35,924

25 claims. l

ThisV invention relates to calling and signaling methods, apparatus and systems, and. more particularly to improvements in the methods, apparatus and systems disclosed patent application of Vaughan, Serial No'` 35,911, filedon June 29, 1948, the same date herewith. and'. issued as United States Patent 2,603,715 on July 15, 1952. Novel features disclosed but not claimed herein may be claimed in said Vaughan application.

The signaling and calling arrangements in accordance with the present invention may be advantageously employed in automatic telephone switching systems wherein a subscriber initiates a call and directs automatic switching equipment at distant switching points to establish connections to the desired called` partys line;

In the calling arrangements commonly employed in telephone switching systems, direct currentis interrupted bymeans cfa dialor other calling device to form direct current or low frequency pulses. This method of calling and signaling is slower than the required time for the operation of automaticv switching equipment so thatv a considerable part of the time of establishing a connection is due to the time required to transmit the calling pulses-to the central oiice.

Furthermore, in the usual systems in the prior art, the direct current or lowA frequency pulses are incapable of being transmitted through and over Voice frequency communication paths.

An object of the present invention is tov provide calling and signaling methods, circuits, apparatus and systems which operate at highv speed and employ pulses capable of being transmitted over voice frequency communication paths of the type normally employed in telephone systems, whereby the time required for establishing connections tlfirouglfz` the switching system` may be materially reduced and the eiiciency of the switching equipment accordingly increased' with the resultantlower cost of establishing each connection therethrough.

More particularly the present invention is directed to methods, systems and apparatus for receiving signaling pulses transmitted at aA high rate of speed over voice frequencyy communication paths from subscribers stations.

In accordance with the exemplary embodiment of the invention set forth in detail hereinafter, the signaling or calling pulses represent subscriber station designations. In the usual type of telephone switching equipment, these designations comprise. a number or frequently an oflice designation of one or more. letters andnumbers followed by still another number. These designations are in turn sometimes followed by another letter or number which is employedto designate a particular party connected to a party line..

It is. of course, possible; to designate'the called subscribers stations by any suitable symbol or group of symbols forming a code or designation.

In order' that these designations may bev more readily referred to, it is assumed that each designation comprises a number of elements which in the exemplary embodiment set forth. herein is eight. Each of these elements is referred. to asa symbol or digit. In order to avoid further ambiguity in descriging the operation of the system in response to` the variousY signals representing thesymbo'lsf or digits, the designation will. be de;- scribed as comprising a number of digital positions, .that` is, eight digital positions inl the. exemplary embodiment set forth herein and each of the digits orl symbols in. each of' the digital positions or symbol positions may comprise a digit of any one of'a plurality of different magnitudes or symbols of different characteristics.

In accordance with the specic embodiment set fortliherein, each element or digital position is: represented by two pulses of short' duration in which the timeA interval elapsing between the two pulses represents the magnitude of the' digit or` the characteristic of the symbol.

Each of the pulses is4 of sufficiently short duration that they may be readily transmitted. over voice frequency communication paths through repeat` coils, filters, amplifiersv and other equipment associated with voice frequency communication paths. These pulses. may also be transmitted through. modulating equipment and' then over carrier current and radio systems the same manner asvoice frequecy currents: as is' well understood by persons skilled in the art.

The arrangeirientr set. forth herein in detail is designed izo-cooperatewith. a, source of such; pulses wherein the pulses representing the number or designationI of ther called stationr is repeated' over and over again" so that the problems of starting the calling equipment at the subscriber station under control of equipment at the central. station are eliminated, Al suitable form of pulse generating equipment iiorY generating pulses at the subscriber station with which: the exemplary embodiment set forth herein is designed tocooperate is disclosedr in" an application of Parkinson, Serial No. 35,930, filed June 29', 1948, the same date herewith and issued as United States Patent. 2,597,898 onzMayZf, 1952.

In systems ofv this type it is necessary te distmguish or recognize the beginning oi' eachv complete station designation so that the digits may be placed in their proper position inthe cal-led subscribersv station designation.. In order that this' may be accomplished, the pulse generating equipment atthc subscriber station is arranged to interpose delays or pauses in transmission between each series of pulses representing a cornplete subscribers designation.

A feature of the present invention is directed to the equipment for recognizing these pauses and for properly conditioning receiving equipment in response to such pauses to receive the following series of pulses designating the called subscriber station.

As set forth in the above-identied application of Vaughan, when pulses of short duration are applied to voice frequency communication paths, they cause transients to appear in the paths at the receiving end, which transients are usually of a decaying or damped oscillating nature and persist for appreciable intervals of time after the applied pulses have terminated. In other words, the application of short pulses to some voice frequency transmission paths having had a low frequency cut-off, which pulses have fundamental and other frequency components suitable for transmission over the voice frequency communication path, are considerably lengthened by the transmission path and related equipment. Thus, if a pulse of a single cycle having a wave form approximating a sine wave and having a duration of approximately a millisecond is applied to such a voice frequency path, an alternating current of decreasing amplitude will be received at the receiving terminal for 31/2 to 4 milliseconds. In order to prevent these alternating currents from interfering with the subsequent pulse, subsequent pulses are not transmitted closer together than approximately i milliseconds. That is, the beginning of one pulse is greater than approximately 4 milliseconds after the beginning of the preceding pulse. At the receiving terminal, pulses are not recognized any closer than about 4 milliseconds apart.

As set forth in the above-identified application of Vaughan, at the reception of a start pulse, which is the rst pulse of any digit of a call designation, a multivibrator or other source of alternating current or pulses is turned or or set into operation and then the number of oscillations or pulses counted until the stop pulse is received.

In accordance with a feature of the present invention, equipment is provided for counting the pulses from the oscillator during the time the transient associated with any pulse is beingV dissipated. Thereafter, the output of the oscillator is switched to a register which comprises another counter so that this counter will count only the pulses designating the actual magnitude of the digit represented by the associated start and stop pulses.

Another feature of the present invention relates to circuits and equipment for counting all of the pulses of a complete subscriber station designation. If the proper number of pulses are received, the equipment stores the magnitude represented by the pulses. If, on the other hand, either a greater or lesser number of pulses than is required to properly designate the desired station are received, the receiving equipment is reconditioned or recycled so that it will respond to the next series of pulses designating the subscriber station. Thus, improperly received pulses are not employed and, consequently, do not cause wrong numbers.

Another feature of this invention relates to circuits and apparatus and methods of operation for picking out or selecting the' desired digital positions of the subscribers designation to control the switching circuits and apparatus at anyl switching position or station.

Another feature of this invention relates to equipment for checking the number of subscribers designations received to determine whether they have been correctly received.

A feature of this invention relates to methods or circuits and apparatus for reconditioning the receiver under either of two conditions:

(1) An improper number of pulses have been received designating a calling station;

(2) Completion of the reception of a station designation and the storing thereof.

Another feature of this invention is directed to circuits, apparatus and methods of rapidly resetting counter and switching circuits between station designations comprising apparatus for generating short pulses including a short-circuited inductance connected in a power supply. means to remove the short circuit and a resistance shunt connected around the inductance to control the wave form and duration of the pulse.

The foregoing and other objects and features of this invention, the novel features of which are pointed out in claims appended thereto, may be more readily understood from the following description of an exemplary embodiment when read with reference to the attached drawings in which:

Fig. 1 shows in outline form various elements of an exemplary system and the manner in which they cooperate oneA with another;

Fig. 2 shows the manner in which' Figs. 3 through 11 are arranged'adjacent one another;

Figs. 3 through l1 when positioned as shown in Fig. 2 show in detail the various circuits of an exemplary embodiment 'of the invention; and

Figs. 12, 13 and 14 show graphs of the potential or currents at various points in the system.

The exemplary embodiment, set forth hereinafter, is arranged to cooperate with pulse transmitting equipment such as disclosed in the aboveidentied application of Parkinson which disclosure is hereby made a part of this application by reference to the same extent as if said Parkinson application was set forth herein in full.

The receiver set forth herein in the following description of an exemplary embodiment is arranged to form a part of a complete telephone system of the type disclosed in Malthaner, Serial No. 35,925, led on June 29, 1948, the same date herewith which issued as United States Patent 2,620,399 on December 2, 1952. The disclosure of the above-identified Malthaner application is also made a part thereof by reference to the same extent as if the disclosure of said application was set forth in full herein.

The receiver described herein is arranged to receive pulses representing the designation of the called subscribers station and store the p0rtions thereof necessary to extend the communication path through its switching center toward the station or ultimate destination of the call under control of the designating code. The usual telephone switching systems of subscribers stations are designated by a multielement designation which usually takes the form of a multidigit number. Frequently the designation includes one or more letters of the alphabet preceding a number and in the case of party lines another letter following the number designating a particular station on a party line.

In accordance with the present system the magnitude of each of the digits of a number is represented by the time elapsing between a start pulse and a stop pulse representing that digit. The various pulses representing all the digits or digital positions of a number, which in the exemplary embodiment set forth herein is eight, are separated by pauses or long blank intervals in transmission in order that the pulses representing each complete number may be readily recognized.

Furthermore, the pulses as transmitted are of short duration and have a fundamental and other frequency components within the voice frequency transmission range so that they may be readily transmitted over voice frequency transmission paths and through the usual type of transmision equipment forming part of such. paths.. Voice frequency transmission paths are usually of limited or narrow frequency range; for example say 300 to 2500 cycles. In transmitting pulses over such paths, it is desirable to select a pulse length having a fundamental frequency component near the midband frequency or near the mean frequency of the pass band. In transmitting pulses of short duration over voice frequency communication paths usually employed in telephone systems, transients are frequently set up which have the effect oi lengthening the pulse at the receiver. These transients are usually in the form of decaying or damped oscillatory waves. For example, in the exemplary system set forth herein pulses having a wave form approximating a single cycle of a sine wave having a duration of apprcxunately a thousandth of a second are applied by the transmitting equipment to the channel extending to the switchingy station. These pulses arrive at the switching station as a prolonged damped oscillatory wave which persists for approximately 31/2 milliseconds.

In order to prevent interference between succeeding pulses, succeeding pulses are not transmitted until after the transient incident to a preceding pulse has been dissipated. In order to allow ample margin in the exemplary embodiment set forth herein the beginning of any two pulses must be at least four milliseconds apart.

In other words, a start or reference pulse is L transmitted and then no transmission take place for four millieconds. Thereafter, a stop or digit pulse is transmitted. This stop or digit pulse may be transmitted in any one of ten different time intervals of a half a millisecond separation. Following the transmission of the stop or digit pulse no further pulse may be transmitted for approximately another four milliseconds. In other words, if the digit interval is measured in increments of approximately a half millisecond, twenty-five such increments are required for each digit. The maximum separation of a start and a stop pulse will then be seventeen increments of time. In order to clearly distinguish the pulses repersenting a complete number or subn scribers designation, it is necessary to separate the pulses representing each such complete designation by a longer interval of time than seventeen increments of one-half millisecond each. In the exemplary embodiment set forth herein this interval of time has been assumed to be of the order of 25 to 50 increments of time, in other words, equal to approximately 1 to 2 times the length of the interval assigned to each digital position of the number.

rThe signaling pulses as transmitted are illustrated in Fig. 12 by the curve or graph |2l. Here a group of start pulses designated S are shown equally spaced, one for each of the digits ofthe subscribers number or designation. etween complete numbers, two intervals each ap.- proximately equal to the time assigned to one digit, designated B in Fig. 12, are blank and. shown at the place where the start pulses would normally occur. However, in order to clearly indicate the beginning and ending of complete station designations these two intervals are left blank so that no start pulses or stop pulses are transmitted during these intervals. It is to` be understood that while two digit intervals are left blank any suitable number or any desired length of blankv interval may be employed so long as it can be distinguished from the intervalsr between the pulses or currents representing the digits of eachy complete station designation.

Each. of the start pulses is followed by a. stop pulsev variably spaced in time from the start pulse. These stop pulses are designated in graph |2| by Nos. 1 through 8. The time of occurrence or transmission of the stop pulse with reference to the corresponding start pulse represents the magnitude of each digit of the subscriber's number or the character of each of the symbols desig.- nation.

The graph |262 illustrates a typical wave form of the pulses as received and applied to the detecting equipment at the central switching station. As indicated by the graph |202, each of the transmitted pulses or signals is appreciably lengthened. As pointed out above, the pulses. are suiiciently spaced in time so that each magnitude of the voltage or currents of. received pulse dies down to substantially Zero before a succeeding pulse is transmitted.

The first line of Fig. 13 shows the last ve pulses of graph |20| on an expanded time scale. Here again the start pulses aredesignated S. The rst stop pulse is designated zero and the second stop pulse is designated 4, the numbers 0 and 4 in this case represent the magnitude of the respective pulses. In addition, the rst graph of Fig. 13 shows the ten possible positions of the stop pulse. For the first stop pulse it is assumed that it is received inl the zero or tenth position and is accordingly shown by solid line. The other possible positions 1 to 9 are shown dotted. Similarly, the pulse in the No. 4 position of the second digit is shown solid since it is assumed that this pulse represents the magnitude of 4. The other nine positions 1 through 3. and 5 through 0 are shown dotted. The graph |302 again shows the wave form of the received pulses as applied to detecting equipment at the central station. Here again it should be noted that each of the received pulses has suicient time to decay to substantially zero before its succeeding pulses or wave train is received.

The receiver set forthA herein, in response to pulses of the type described above representing a subscribers station designation, selects and stores pulses representing the magnitudes of the digits of the designation or number which are to be employed at the switching center in extending the communication path towards the station of destination of the call.

In order to set the system in operation relay H4 is operated either manually of automatically. However, for purposes of illustration, assume that relay ||4 is operated by operation of key |61.

Relay im in operating removes the terminating resistor |56 from the incoming line ||2 and connects the line to the terminating equipment |2d` which comprises a band-pass lter |20 and volume limiting or regulating amplifiers and the pulse shaping equipment.

The incoming line H2 usually comes through switching equipment from any one of the large number of incoming lines or trunks. These lines or trunks are frequently provided with suitable types of terminating equipment of various kinds, depending upon the type of incoming line or trunk. The incoming line or trunk may comprise open Wire lines, cable circuits, carrier trunk channels, radio channels or any other suitable type oi voice frequency communication path or any combination of any such type of paths. Each of thepaths may include various types of associated Ysupervisory and regulating equipment which necessary or desirable to the proper transmission of the signals over the path. By terminating the path in a terminating resistor prior to connection to the receiving equipment noise and stray currents are reduced within the path and prevented from interfering with the operation of the receiving equipment. Consequently, both the receiving path and receiving equipment will be in proper condition to be connected together upon the operation of relay iid. Inasmuch as receiving equipment may be connected to any one of the large number of incoming lines as described in greater detail in the above-identied application of Malthaner, it is advantageous to first transmit the signals through a volume limiting or gain controlled amplier, as is described herein.

Relay I4 in operating also conditions the volume limiting equipment |22 so that it will operate to control the gain and thus the amplitude of the output from this amplifier. The operation of relay H4 also operates the message register H8 to register a call and interrupts the operating circuit to relay i6.

Relay H in releasing conditions a code detector 535 in the start circuit |34 for operation.

From the volume limiting amplifier |22 pulses are ampiiiied by the amplifier |28 and then applied to the digit detector |30 and the code detector 35. At this time the digit detector |38 is blocked so that it does not respond to the pulses received through amplifier |28. The code detector |35, however, responds to these pulses and repeats them to .the blank interval timer |36. Blank interval timer |36 is provided to recognize the long time or blank interval between the pulses representing each complete subscribers designation or number. When no pulses are received .for period of time equa-l to the time assigned for between 1 and 2 digits of a number, the blank interval timer will respond and condition the digit detector i3d to respond to the subsequent pulses. Thereafter, the digit detector |35.l will respond to the succeeding pulses which are the first pulses of a complete subscribers station designation. The output of the blank interval timer is also applied to steering circuit |5| and conditions this circuit for further response to pulses as will be described hereinafter.

The rst pulse received by the digit detector causes the disabler |3| to again disable the digit detector |30 for a short interval of time of approximately 231/2 to fi milliseconds. Thus the digit detector responds to and repeats the first pulse or wave of current of a given polarity applied to it and thereafter is disabled until the transient which arises incident to the transmission of a pulse has been dissipated. During the time the digit detector is disabled, the system is substantially unaffected by noise and stray cur- S rents. Consequently, the operation in the presence of stray currents is improved.

Thereafter the digit detector |30 and disabler |3| operate in a similar manner on each of the succeeding pulses. In this way the transients of one pulse are prevented from interfering with a succeeding pulse.

The first pulse from the digit detector |35 is also applied to a switching circuit called a square wave generator designated 32. The square wave generator |32 connects or sets into operation an oscillator or other source of varying current. This source |33 is called the timing multivibrator in Fig. 1. The switching circuit |32 also controls another switching circuit |55 as will be described hereinafter.

The output of the timing multivibrator |33 is transmitted through an electronic switch |59 to a counter |58. Counter |58 is arranged to count seven pulses and then be restored to its original condition. The output of the oscillator |33 or other suitable pulse source is arranged to transmit currents or pulses at the rate of one for each increment of each time interval assigned to a digit. Thus during the increments assigned to a start pulse, seven pulses are transmitted by the timing multivibrator |33 during the remainder of the transient of the rst start pulse. These pulses are counted by the seven counter |55 shown in Fig. l. At the end of this time the switch controlling circuit |57 actuates the electronic switch |59 so that the succeeding pulses from the source l3-3 are transmitted through the electronic switch |59 and through the digit steering circuit |5| and then to the proper digit counter |53. Thereafter, the number of pulses transmitted from the timing multivibrator |33 to counter A is in accordance with the magnitude of the rst digit of the number. Counter A designated |53 in Fig. 1 thus counts these pulses so that the magnitude of the first digit may be recorded. If the magnitude of the first digit is one, the stop or digit pulse will be received over line H2 during the next pulse interval after the end of the count of 7 by the seven counter |58 so that only one pulse will be transmitted to and counted by counter |53. If the digit has a magnitude of say ve then counter |53 will count iive pulses before the stop or digit pulse is received over line ||2. Upon the receipt of the digit or stop pulse over line ||2 the digit detector |30 will respond to this pulse in the manner described above and cause the switching circuit or square wave generator |32 to be actuated which in turn stops or disconnects the source of current |33 and prevents any further pulses being generated or ,transmitted by this device.

Upon the reception of the next start pulse the circuits in converter operate in substantially the same manner as described above. In this case the start pulse is repeated by the digit detector |30 which is thereupon disabled for the desired interval of time. The output of the digit detector |35 again actuates the switching or square wave generator |32. This generator again connects or activates source |33. In addition, the switching circuit |32 causes the steering stepping circuit |50 to be advanced one step so that the succeeding pulses will be counted and recorded by the counter |54 of binary counter |52. Here again the first seven pulses are counted by the seven counter |58 and each succeeding pulse is then transmitted through the steering circuit |5| to the B register designated |54 in Fig. 1. In a similar manner, pulses representing each of the sucrepresenting -all digital positions of va subscribers designation to respective counting and storing circuits. Thus, in the .case of an .eight .digital position designation, the steering circuit will direct or distribute pulses representing the .magnitude in the Adigit in each of the digital positions of the proper one of .the eight counting .and storing circuits.

Three digital counters |53, |543 and ,|55 .are shown in the drawing. These are shown merely by way of example to show the posit-ion .Qi the counting and storing .circuits in the system and the manner in which they cooperate with the other circuits of the system. These counters represent .any suitable .or necessary number of counting circuits .from 'one to la maximum number of digital positions in a complete subscribers designation. When, as in the usual case, it .is only necessary to use a portion of the digital .positions of a subscribers designation at any one switching center the counting circuits |155, |513 and |55 represent that portion which it is necesary or desirable to use at any one switching center. This portion may comprise the rst one or more ldigital positions, one or more intermediate digital positions or .one .or ,more of the final digital positions .of the subscribers vstation designation. Also the counters as shown in the drawing may be employed .to count and store pulses representing the magnitude of the .digits in either consecutive or non-consecutive digital positions of the complete subscribers designation.

The output from the digit .detector .|39 is also applied to sixteen pulse counter lll-7. The six.- teen pulse counter -Ifil is employed `to .count .each of the output pulses from the .digit `detector |30. In the exemplary embodiment set forth herein there should be exactly sixteen pulses representing each subscribers designation because two pulses are required to represent each vdigit or digital position o f the subscribers identifying code and -eight such digits a-re employed in each subscribers designation. In other words, there should be sixteen pulses received between each of the blank intervals between the pulses representing a complete number or subscribers designation.

If at the time the second blank interval is recognized by the blank interval timer |35, sixteen pulses `have been received, the locking circuit |42 is set into operation and in .turn causes the operation of the relay H5 through the cath ode follower circuit ldd. The relay l5 in operating completes an obvious circuit for the operation of relay |75 and interrupts the operating Circuit of relay lili and also causes the setting of the binary counters |53 through |55 to be stored in the storing circuits |53 through |53. Thereafter when desired, the number registered or stored in the storing circuits may be checked by checking relays |54 and the appropriate correct or error registers .|55 .and it, respectively, operated.

The operation of relay ils removes the short circuit `from around .the inductanee |76 .thus in-Y serting this inductance in the lbattery supply lead extending to the sixteen pulse counter mi and the .switching or square wave generator |32 .and possible other circuits. lThe insertion of this in .ductance causes `the current to be momentarily reduced to a very low value Similar to interruptl0 ing .the circuit for a controlled short interval and thus in eiect causes anegative lpulse to be applied .to the battery .Supply lead extending .to the above-mentioned circuits. This pulse has the elfect ci restoring these circuits .to their initial condition wherein they are ready to respond ,toA

more received pulses.

The operation o f either of the .registers |65 or |65, assuming the keys |61 and |68 in the vset are as shown, .completes a circuit for the operation of relay which relay in turn causes the operation of relay lll. Relay |11 interrupts the short circuit around inductance in the battery supply lead of the binary counter circuit |52 as well ascircuit |58 and the locking circuit lei .thus .causing all of these circuits to return to their initial condition.

`I f either a Agreater or lesser number of pulses than sixteen is received between the two blank intervals or if the receiving circuits respond in such a manner that more or less than sixteen pulses are transmitted to the sixteen-pulse counter .|47 between two blank intervals as recognized by the blank interval timer i 36 the entire receiving equipment will be recycled .upon reception of the second blank interval. Ifcircuit |36 responds to a second blank interval at a time when .the sixteen-pulse counter |41 does not indicate a count of sixteen the recycle circuit |d3 is controlled by the counterreader |138 and causes the recycle relays '13 and |12 to be operated through the cathode follower circuit |45. .Operation of the recycle relay |l2 causes La recycle register |69 to operate. As shown in Fig.. V1 a subsidiary locking circuit is provided for relay |12 under control of the recycle register .l 59 which insures that the register will completely operate each time the relay |12 operates.

.Relay |13 in operating removes the short circuit from .around both the induotances 1c and |71 and thus resets all of the above-.mentioned circuits without causing .the setting of the digit counters |53, 54 and |55 to be .transferred to the digit storing circuits IGI, |52 or |63, Thereafter the receiving circuit operates asdescribed above in response to the succeeding series of pulses representing .a called subscribers station or designation. 4Ir" `sixteen pulses are received bythe sixteen-pulse counter for this .series of pulses the setting on the digit counters will be transferred to the digit registers or storing devices as de.- scribed above, .I f on the other hand a different number of pulses is counted `by the sixteen-pulse counter the circuits will be recycled `again as described above..

The manner in which the abcve-described circuits function may be more readily understood from the Afollowing `description when read with reference to Figs. 3 to l1 as arranged adjacent to one another in a manner shown in Fig.. 2.

Reference will also be made to Figs. 12, 13 and 14.

Fig. 3 shows the limiter circuit designated I 24 in Fig. l. In addition, Fig. 3 illustrates in a general way the manner in which the subscriber ystation is connected to the input circuit of the receiving equipment. The ,Subscriber station is indicated at 3|il .as being connected .over aline 3|? to a 4central switching station having .terminal and switching .equipment 3|3. The subscribers station maybe in accordance with the disclosures of the above-.identined patent aprilie cation of Parkinson or accordance with .the disclosure of the above-identified patent application of Malthaner or in other suitable subscribers station equipment.

Line 3 i 2 may comprise any suitable type of subscribers line providing a voice frequency transmission path of from approximately 75 cycles to 1950 cycles, or higher. The usual subscribers line provides a voice frequency transmission path having greater frequency range.

The terminal and switching equipment 3|3 may comprise any suitable type of line terminating equipment at a central switching station as well as any suitable type of switching equipment. The switching equipment shown in the aboveidentied patent application to Malthaner which in turn shows equipment of the type disclosed in Bruce et al. Serial No. 782,702, led October 29, 1947. This equipment may also include other types of switching equipment such as so-called panel type systems or crossbar systems when so desired. The receiver equipment described herein in detail will cooperate equally well with all of these various switching systems as will be readily understood from the following description.

The incoming line, after passing through the terminal and switching equipment 3|3, is normally terminated by resistor |063 connected to the break contacts of the relay |062.

The gain of the limiting amplifier shown in Fig. 3 is normally maintained at its maximum value due to a circuit extending from ground through the inner upper break contacts of relay |062 and resistor 321 to the center point of the input transformer secondary 3|5 as well as the connections through the condenser and resistance network 32B and the voltage dividing network 329.

When it is desired to condition the receiver for receiving pulses relay |062 is operated by the operation of the key contacts I4 or |||5 or automatically under control of switching circuits as set forth in the above-mentioned application of Malthaner.

The operation of relay |062 at this time removes the terminating resistance |063 from the incoming line and connects the line to the bandpass filter 320. Thereafter incoming signals from the terminal equipment 3 I3 are transmitted through the filter equipment 320 to the terminating resistance 3|4 and the input transformer 3|5. The terminating filter 320 may be of any suitable type and is provided to prevent power supply frequencies, which may be supplied over the line 2 to operate the equipment at the subscribers station, from interfering with the operation of the receiving equipment of the exemplary embodiment set forth herein in detail. In addition, the filter equipment 320 is used to shape the pulses so that pulses arriving over different subscriber-s lines will all have similar shapes so that the receiving equipment will respond to the received pulses substantially the same and independent of the subscribers line over which they arrive. Filter 320 also prevents extraneous noise and high frequency currents from interfering with operation of the receiving equipment.

Transformer 3|5 is a push-pull input transformer and applies the incoming pulses to the control grids of tubes 3|6 and 3|`| in phase opposition. Tubes 3|6 and 3| 1 comprise a pushpull amplifier and repeat the incoming pulses through the output transformer 3|8 to the terminating resistor 340 and the conductors 34| extending to Fig. 4. The input winding of transformer 3|9 is also connected across the terminating resistor 340 and repeats the signal output from the push-pull amplifier comprising tubes 3|6 and 3H to the grid circuit of tube 32 l.

The grid of tube 32| is normally biased by voltage divider 330 so that substantially no current flows in the anode-cathode circuit of this tube unless positive pulses are applied to the grid from transformer 3| 9. So long as the amplitude of the pulses applied to the transformer 3I9 from the output of tubes 3| 6 and 3H is below a predetermined minimum value the gain of tubes 3|6 and 3|'| is maintained at a maximum value due to the grid potential supplied to the center point of the secondary winding of transformer 3|6. However, when the amplitude of the pulse output from this amplifier as applied to the transformer 3|3 to the grid of tube 32| exceeds the predetermined minimum value as determined by the voltage divider 330 positive pulses will be applied to the control grid of tube 32| thus causing current to ow in the output circuit of this tube.

When current fiows in the output circuit of tube 32| the anode potential of this tube will be reduced and in turn reduce the input voltage applied to the grid of tube 322. Tube 322 acts as a cathode follower tube and tends to repeat the potential applied to its grid in its cathode circuit. Thus, when the grid becomes negative as described above the cathode of tube 322 also becomes more negative than previously. The cathode of this tube is coupled to the rectiiier tube 325 through the coupling condenser 320. Coupling condenser 324 and related resistors have a long time constant so that the potential applied to the cathode of rectier 325 follows the potential of the cathode of tube 322 with I the desired accuracy. The application of a negative pulse or potential to the cathode of the rectier tube 325 causes current to flow through tube 325 which in turn tends to discharge the upper terminal of 326 so that this terminal becomes more negative thus decreasing the bias voltage applied to the control grids of tubes 3|6 and 3H thus reducing the gain of these tubes.

'I'he time constant of networks 326 as well as the other circuit elements are such that it requires several pulses to properly control potential of the control grids of tubes 3I6 and 3H and thus to control the gain of the amplifier tubes 3|6 and 3|'|. At the end of several pulses the gain of the amplifier will become constant and will be of such a value that the output pulses will have substantially the same magnitude independently of the magnitude of the received pulses and thus independent of the length of line, transmission characteristics and the line of the incoming subscribers line.

The operation of relay |062 also completes an obvious circuit for the operation of the register |064 which counts or records the total number of calls handled by the receiving equipment described herein. The operation of relay |062 also connects the short circuit around the inductance coils |054 and |053. This short circuit, however, does not materially affect the current ilowing in these leads thus does not materially affect the operation of the system because the resistance in these coils is relatively low and a relatively insignificant part of the resistance of the load circuits supplied through the inductances |053 and |054.

The operation of relay |062 also interrupts the circuit 0I the normally operated relay |06| this permitting relay lto release, Release of .relay |06| at this time partially conditions other circuits which will be described hereinafter and, in addition, provides a locking circuit for main:- taining relay |062 operated under control of re lay |015.

Relay |6l, in releasing, also removes ground from the upper terminal of condenser l524 .of the start circuit shown in the lower portion of Fig. 5 and designated |34 of Fig. 1 thus conditioning this circuit so that it will respond to .the .received pulses. The start circuit shown in the lower por, tion of Fig. 5 is arranged to Vrecognize the blank intervals, that is, the pauses between each series of pulses representing a complete subscribers station designation or number.

The polarity of the output rfrom the output transformer 3H;` as applied to conductors 34| is shown by the graph |325. These .pulses or cur.- rents are applied to the grid of tube 4|0 and after repeating and amplication by tube M0 they appear as positive pulses or of opposite polarity at the anode of tube 4|0. `These pulses are then applied through two coupling networks to one of the grids of each of the tubes 4 I y| and 52.0. Tubes 4H and 520 are gaseous discharge tubes .and are arranged so that they are normally not conducting. Tube 4H has biases applied to both of the control grids so that under normal conditions and except as will be described more fully hereinafter the application of positive pulses to the first grid of tube 4|| will not create a discharge through the tube.

Tube 52o, however, has its second grid cone nected to ground potential and thus this grid is only a few volts negative with respect tothe cathode. As a result the application of each positive pulse to the control grid of tube 520, vWhic-h ex ceeds a predetermined magnitude, causes a dise charge through this tube providing suilcient anode potential is supplied to the tube. As described above, the release of relay 06| removed ground potential from the anode of tube 520. Thereafter, tube 520 will respond to the positive portions of each of the pulses applied to its con trol grid and in turn causes negative potential to be applied to its anode due to the anode resis tor or Vthis tube. Between -theapplieation of -positive pulses to the control grid of tube 529, the upper terminal of condenser 524 will start to charge to -a positive-potential through the anode resistors of tube 52D and the inductance 525 and its shunt resistor.

Normally, the right-hand section ei' tube 52| and the left-hand sections .of tubes '522 and 523 are conducting while the other section of each `of these tubes is not conducting. Similarly, `the lefthan-d section of tube 4|2 and the Aright-hand section of tube 4| 3 is likewise conducting current while the opposite sections are not.

Upon the application of the positive portions of cach lreceived pulse to the control grid of 520 after the release of relay |06I, a discharge is initiated through the gaseous conduction tube 525. This discharge causes condenser 524 to be discharged. The condenser 524together with the inductance of 525 and its associated shu-nting resistance are so related one to another and to the tubes and -voltages `applied to the circuit `that the upper terminal of condenser 524 will be sufflciently discharged each time tube 520 kbecomes conducting that the discharge through tube 520 is extinguished. In other Words, these elements form an oscillating circuit but current will flow for a `portion only of one cycle vof Athe osciliation for .each discharge throughtube .5.20 .and then.

extinguish the tube. resistance .shuntine the znductance `5.25 is `provided to rapidly damp out the oscillation the circuit comprising in ductence 5.25 .and .condenser 524 so that substantiaily only .a fraction ci a cycle flows in .the .outout .circuit for cach discharge through the tube..

The above-described .operation is repeated for each received pulse until the silent interval or pause between pulses representing each complete subscriber station designation. At this time no pulses will be received fora sufciently long interval .of time so the upper terminal of condenser 524 will .receive .a slliliciently .high positive poten tial to initiate a discharge of current through the .leftfhand section of tube .52 l.

The above described .operation in the start circuit is illustrated in Fig. 12. When the am.- plitude .of the received pulses or current from the volume limiting amplier of Fig. `3 crosses the bias line designed |2|'3, the amplified currents from tube All). will be of suicient magnitude to initiate a discharge through tube 52|. Each discharge through tube 52| causes current to flow through the tube, `discharging the upper terminal of condenser 524. The graph I2|4 of Fig. 12 represents the current flowing through tube .52|.

Graph |205 `illustrates the voltage of the upV per `terminal of condenser 524. As shown by the graph |255 the voltage of the upper terminal condenser 524 falls to a relatively low and fixed value upon each discharge through tube 52|. Each discharge through tube 520 is terminated by the action of the gas conduction tube, inductance 525, and condenser 52.4. At `this time the upper terminal .of condenser 524 starts to charge through resistor 528 and thus its voltage rises. The time during which this voltage is permitted to rise determines the Ymagnitude ofthe voltage. The charging action and discharging action 'in the circuits is illustrated by the irregular saw.- tooth curve |205, Fig. "12. Each one of the teeth are of 'intermediate amplitude until after the reception of the eighth st op pulse as shown in Fig. VAl2. After this pulse is received no further pulses will 'be received Ifor the two blank intervals with the result the upper terminal of condenser of 524 will charge for a longer interval of time and reach an appreciably higher voltage. When the voltage of the upper terminal of condenser 524 exceeds a reference voltage indicated by line |256, 12, current is initiated through the left.- hand section of tube 52| which current continues until 4the first start pulse representing the next complete subscribers number is received. At this time a discharge is again initiated through tube 529 which in tur-n discharges the upper termina-l of condenser 524 and interrupts the current through the left-hand section of tube 52|. The graph |201 represents .the Current QWins through the left-'hand Section of tube 5.2 I.

When .current ystarts to now through the lefthand section of tube 52E, the anode potential of 15,111.5. section will .fall and apply a negative potential through the coupling condensers to the cone .trol grids -Qf the rehtfhahd section of tche .52! and the left-hand `.section .of tube 522.

The Anegative potential or pulse from the anode of the lleft-.hand section of tube 52|, when this section starts to conduct current, is also applied to the control grid of the left-hand section of tube 523. However, .condenser 521 conneoted'between thenontrol grid and .the .cathode orground of :this tube provides .a pulse .lengthening means 15 so that the response of this tube at this time is retarded a short interval of time.

The negative pulse output from the left-hand side of tube l52| is also coupled to the grid of the right-hand section of tube 523. However, this section of tube 523 is normally biased so that the tube will not repeat the pulse applied to its grid at this time. After the termination of the pulse as applied to the grid of the right-hand section of tube 523 as determined by the constants of the coupling circuit, the left-hand section will respond to the lengthened pulse due to condenser 52T which interrupts the current flowing through the left-hand section of this tube. When the current flowing through the left-hand section of tube 523 falls, the voltage drop across the anode resistor also decreases so that the anode potential rises and applies a more positive bias to the control grid of the right-hand section of this tube so that upon the application of the next negative pulse from the left-hand section of tube 52| the right-hand section of tube 523 will operate as an amplier and repeat a positive pulse in its output circuit as will be described hereinafter.

When a current flowing through a left-hand section of tube 522 is interrupted, the potential drop across the cathode resistor common to both sections of this tube falls to a low value which in eiect makes the potential difference between the cathode and the control grid of the righthand section more positive so that current will start to flow through the right-hand section of tube 522. Current flowing through this section causes the potential of the anode of this section to fall in value which in turn applies a sufficiently negative grid potential to the left-hand sections of tubes 522 and 523 to maintain these sections non-conducting unitl some further potential is applied to the system to alter their conducting conditions as described hereinafter.

When the left-hand section of tube 52I becomes conducting during the blank interval as described above, a negative pulse of short duration is applied through the coupling condenser 722 to the control grid of the right-hand section of tube TIB. This tube is normally conducting so that the application of a negative pulse to its control grid causes a positive pulse to be repeated in the output circuit of the right-hand section of tube TIG. The output circuit of the right-hand section of tube lIS is connected through the coupling condenser '|23 to the control grid of the gaseous conduction tube 'l I5. The application of positive pulse to the control grid of tube 'H at this time initiates a discharge through tube I I 5. The discharge owing through tube 'H5 will thereafter continue until interrupted as described hereinafter. If a discharge had been ilowing through tube 1M prior to the initiation of a discharge through tube 'H5 the initiation of the discharge through tube 'H5 will momentarily raise the potential of the cathode of tube 'IIA above the potential of its anode and thus interrupt the discharge flowing through tube I4. The discharge flowing through tube 'H5 causes its cathode to rise in potential and condition tube 'HI to have a discharge initiated through it upon the reception of the lirst start pulse of the succeeding pulses designating a called subscribers station as will be described hereinafter.

Upon the application of the iirst pulse following the blank interval between the pulses representing a complete subscribers station desig- 75 nation, a discharge is again initiated through tube 52@ whereupon the upper terminal of condenser 522 is again discharged and a negative potential applied to the control grid of the lefthand section of tube 52|, thus interrupting the current through this tube and causing current to be initiated through the right-hand section. Thereafter, the circuits respond as described above to each succeeding pulse applied to the control grid of tube 526 which therefore maintains the upper terminal of condenser 524 eiiectively discharged so that the left-hand section of tube 52| remains non-conducting and the right-hand section conducting. Likewise the right-hand section of tube 522 remains conducting and holds the left-hand sections of tubes 522 and 523 non-conducting.

When current ceases to flow through the lefthand section of tube 522 during the blank interval as described above, the potential drop across the resistor Q22 common to the anode circuits of the left-hand section of tube 522 and the righthand section of tube lI|2 is greatly decreased thereby raising the potential applied to the upper terminal of the upper resistor M9. As a result a more positive bias is applied to the second grid of tube SII so that upon the application of the succeeding positive pulses to the control grid of tube 4I I, from the output of the tube MEI, discharges will be initiated through tube 4I I.

The first pulse following a blank interval will be the start pulse of the rst digit or rst digital position of the called subscribers number or designation. This pulse may represent either a numeral or a character of the alphabet or some other symbol as may be desired. Upon the initiation of a discharge through tube liII in response to this pulse, current flows in the output circuit of tube 41| thus lowering the anode potential and applying a negative pulse through the coupling condensers M5 and M6 to the circuits of tubes M3 and M2. The output circuit of tube 4II also includes condenser Il which together with the anode resistor form an oscilr lating circuit for extinguishing the discharge through tube 4H when condenser 4I? becomes suiciently discharged.

The application of a negative pulse to the control grid of the left-hand section of tube 4I2 through the coupling condenser 4I6 interrupts a current flowing through the left-hand section of tube 4I2. The magnitude of the coupling condenser 4|6 and the biasing resistor associated with the grid of the left-hand section of tube 4I2 are chosen to apply a pulse of very short duration to the control grid of the left-hand section of tube 4I2 in response to each discharge through tube 4I I. Such circuits are sometimes called diierentiating circuits.

Upon the interruption of current flowing through the left-hand section of tube 4|2, its anode potential rises and applies a positive potential or pulse through the coupling condenser 426 to the control grid of the right-hand section of this tube whereupon current starts to flow y through the right-hand section of tube 4|2 which in turn decreases its anode potential so that a negative pulse is applied through the coupling condenser 423 to the control grid of the left-hand section of tube 4I2 and thus tends to maintain the left-hand section of this tube non-conducting.

As described above, when current starts to flow through the right-hand section of tube 4I2 its anode potential falls to a relatively low value and 

